1. Field of the Invention
The present invention relates to a substrate processing method and a substrate processing apparatus, more specifically, a substrate processing method and a substrate processing apparatus for processing substrate-to-be-processed, such as semiconductor wafers, LCD glass substrates or others, held in an atmosphere sealed processing vessel with a processing gas, such as ozone, etc., fed into the processing vessel.
2. Related Background Art
Generally in fabricating a semiconductor device, a series of processing steps of applying a photoresist to a semiconductor wafer, an LCD substrate or others (hereinafter called a wafer or others) as a substrate-to-be-processed, the step of diminishing a circuit pattern by photolithography, transferring the circuit pattern to a photoresist and developing the circuit pattern, and the step of removing the photoresist from the wafer or others is conducted.
One example of the above-described processing will be explained with reference to FIGS. 1A to 1H by means of a case where a substrate-to-be-processed is a silicon wafer. First, a thick oxide film OX1 is formed on the surface of a silicon wafer W (hereinafter called a wafer W) (the first oxide film forming step: see FIG. 1A). Then, a resist is applied to the surface of the oxide film OX1 to from a resist pattern RP1 (the first resist pattern forming step: see FIG. 1B). Next, an unnecessary portion of the oxide film is etched off with a chemical liquid, such as DHF (HF/H2O) or BHF (the first etching step: see FIG. 1C). Then, the resist, which is unnecessary, is released with a chemical liquid (sulfonated water), a mixed liquid of SPM (H2SO4/HEO2) (the first resist removing step: see FIG. 1D). Next, a thin oxide film OX2 is formed on the surface of the wafer W from which the unnecessary resist has been removed (the second oxide film forming step: see FIG. 1E). A resist is again applied to the surface of the oxide film OX2, and a resist pattern RP2 is formed (the second resist pattern forming step: see FIG. 1F). An unnecessary portion of the oxide film is etched off with a chemical liquid, such as DHF (HF/HEO), BHF or others (the second etching step: see FIG. 1G). Finally, the resist, which is unnecessary, is released (the second resist removing step: see FIG. 1H).
In a conventional cleaning equipment used as the above-described resist removing means, generally wafers, etc. are immersed in cleaning tank filled with a chemical liquid, such as SPM (a mixed liquid of H2SO4/H2O2) (sulfonated water) or others to remove the resist films.
However, when sulfonated water is used as the chemical liquid in the first resist removing step (see FIG. 1D), sulfuric acid ions remain on the surface of the wafer W after the resist has been removed, and there is a risk that the residual sulfuric acid ions may become a cause for particles and cause contamination. Furthermore, the residual sulfuric acid ions also causes an uneven thickness and poor film quality of the thin oxide film formed in the following second oxide film forming step (see FIG. 1E).
On the other hand, recently, it is required ecologically to removed the resist with a solution of ozone (O3), whose waste fluid is easy to treat. In this case, the so-called dip cleaning, in which the wafers or wafers or others are immersed in a cleaning tank filled with a solution of ozone, is used, so that the resist is oxidized with oxygen radicals in the solution to be decomposed into carbon dioxide, water, etc.
The above-described solution is generally prepared by bubbling and dissolving a high concentration of ozone gas into pure water, and later the thus prepared solution is filled in a cleaning tank. It is often that meanwhile ozone in the solution is decomposed, and the solution has the ozone concentration decreased, and a sufficient amount of ozone cannot be supplied to the resist surface. High reaction rates cannot be provided.
Then, in place of the dip cleaning, in which the wafers or others are immersed in a solution of ozone, it is proposed to use a processing gas, e.g., ozone, and a vapor, e.g., steam, as a solvent to remove the resist from the wafers or others. In this cleaning method, a processing gas, e.g., ozone gas is fed to the wafers or others held in a tightly closed processing vessel to thereby remove the resist from the wafers or others. The use of ozone and steam is free from the residual sulfuric acid ions, and accordingly can improve thickness evenness film quality of the thin film. In this case, ozone is generated by ozone generating means which mixes oxygen (O2), a base gas as a raw material with nitrogen (N2) while being discharged.
However, this ozone gas contains nitrogen as described above. As the ozone gas is fed, the nitrogen also flows into the processing vessel to contact the wafers or others. When nitrogen contacts the wafers or others, the nitrogen reacts with the ozone gas to corrode and etch metals of aluminum (Al) and tungsten (W) of the wiring portions, causing particles. This problem of the metal contamination and particle generation is the case also with the wafers or others which have not been subjected to the wiring step.
The processing with ozone gas containing nitrogen excessively oxidizes the wafers or others with NOx- or HNOx-based atmospheres (chemicals), and chemical oxide films grow on the surfaces of the wafers or others, possibly causing thickness unevenness and poor film quality of the thin oxide film.